Video Brightness Control for acpid

video-brightness.sh

#!/usr/bin/env bash

bl_dir='/sys/class/backlight/intel_backlight/'
bl_dev="$bl_dir/brightness"
bl_index='/var/acpi/backlight/index'

max_brightness="$(<"${bl_dir}/max_brightness")"
min_brightness=82

min_index=0
max_index=12

index="$(<"$bl_index")"

(( step = (max_brightness - min_brightness) / (max_index - min_index) ))

case "$2" in
	BRTUP)
		(( index = index + 1 ))

		if (( index > max_index )); then
			(( index = max_index ))
		fi
		;;
	BRTDN)
		(( index = index - 1 ))

		if (( index < min_index )); then
			(( index = min_index ))
		fi
		;;
esac

echo -n "$index" > "$bl_index"
echo -n "$(( index * step + min_brightness ))" > "$bl_dev"